It played a key role in late Mideval and early modern British history and is a mentioned as one of the basic rights of Americans in the original, unamended Constitution of the United States. In fact, in the original 1787 Constitution that made almost no restrictions on the powers of the states, it is mentioned as being something that the states cannot do.

The concept is “attainder” and it is difficult to understand either British or American history without understanding what it is. To be “attained” is to be legally “singled out” for punishment. The “bill of attainder” prohibited by the U.S. Constitution (Article I, Section 9 (Congress) and Section 10 (the states)) refers to the legislative process of passing a law that singles out an individual or group of individuals for punishment. (Thus, bills of attainder are mentioned in Article I, the article about legislative powers.) Attainder laws are closely related to the concept of ex post facto (after the fact) laws. The founders of the U.S. were concerned about the separation of governmental powers: legislative, executive, and governmental. Decisions about crime and punishment, in their plan, ultimately came under the purview of the judiciary. Congressional attainder would have upset that balance between the three branches of the American government. It would have allowed the heat of public opinion to convict people of crimes via attainder, even if the courts ruled them to be not guilty. The prohibition against attainder remains a check against any possible “tyranny of the majority” against individual citizens, even though most Americans aren’t now aware of this. (James Madison argued in favor of outlawing laws of attainder in Federalist No. 44, arguing that they were “contrary … to every principle of sound legislation”.)

In the history of England, attainder was the ultimate legal sanction against a treasonous noble. Before the Tudor dynasty of kings and queens (1485-1603), during the Hundred Years War and the War of the Roses, most of the men who held any significant position of authority in the English government were also peers (lords) of the realm. The word peer originates from the Latin word par (meaning “equal”). Peers (dukes, marquesses, earls, viscounts, and barons) inherited their titles and associated privileges from their fathers, usually according to rules of strict male-line succession. Though dukes have the highest honor (precedence) amongst all of the peers and barons the lowest, all peers of the realm are in a sense equal (“on par”) with one another, as each one had an equal vote in the House of Lords. They were, in a sense, born into the family business of assisting the king in ruling his kingdom, and each one had the legal privilege of direct access to the sovereign. If a peer rebelled against the king and was arrested, the king could demand that Parliament pass an act of attainder against the peer. This act would revoke the title of the rebel lord. This revocation would also end the possibility of passing on that title to anyone else (son, grandson, nephew, etc.). Essentially, the title was “put to death”. An attained lord was thus reduced to the status of a commoner, and subject to punishments for commoners, such as burning at the stake. Since only peers were leaders of the body politic in pre-Tudor England, demotion from the peerage effectively ended a career in high politics, even for those who escaped the fate of execution after attainment. Those rebel peers who were killed in battle could still be attained after the fact (ex post facto).